fairly?!

[hooshdar3]

"Two kinglets huddling together were found to redude their heat losses ----------- by a quarter and three together saved a third of their heat.

1)fair noticeable 2)fairly noticale 3)fairly noticeably 4)fair noticeably

I marked 3, but The answer sheet gives 2.I feel 3 is correct, but I didn't find proof that adv. + adv. is possible.Is my feeling wrong?

[Barb_D]

You are correct. It is reduced, a verb, so it's noticeably. How noticeably? Fairly noticeably.